Damping sheets are normally employed in vehicles, in particular in motorcars, in order to decrease vibration during driving. Usually, they are placed or tentatively fixed upon the car floor or the steel panel such as dash panel and then fixed permenently by fusion with heat. Such sheets are prepared by melting one or more binder components which are, for example, asphalt (e.g. straight asphalt), natural or synthetic rubbers and/or various synthetic resins, then by incorporating into them fillers, namely a fibrous filler (e.g. asbestos) and a powdery filler (e.g. calcium carbonate, talc or diatomaceous earth), by blending and mixing the composition, then by rolling it to give a sheet, and finally by cutting it into desired shapes.
While asbestos is a suitable fibrous filler in order to impart tensile strength and rigidity to the damping sheet, it is quite harmful for humans and use thereof is going to be prohibited in view of public interest in health.
Therefore, there is strong need for compositions containing fibrous fillers, alternate to asbestos, that may give desired mechanical properties to the damping sheet.
Compositions suited for the damping sheet containing an organic filler are known, for example, in Japanese Patent Kokoku (that is to say Application published for opposition) Nos. 52-50522 and 56-5469. Kokoku No. 52-50522 discloses a composition for damping sheet that comprises 45-65% by weight of asphalt, 8-18% by weight of an organic fiber having the fiber length 0.5-5 mm and the section diameter less than 100 .mu., 20-35% by weight of a filler and 1-5% by weight of an asphalt denaturing agent Kokoku No. 56-5469 discloses a composition for damping sheet that comprises 45-65% by weight of asphalt, 8-18% by weight of an organic fiber having the fiber length 0.5-5 mm and the section diameter less than 100 .mu., 18-37% by weight of dust consisting mainly of silicon dioxide and 1-5% by weight of an asphalt denaturing agent.
Although the prior art compositions were able to replace asbestos by an organic filler, their characteristics were not fully satisfactory due to the use of somewhat excessive amount of the organic filler having quite a long fiber length and to the absence of quick lime as a part of an inorganic filler, as will be described hereinafter in detail.